It is common to stack cardboard/corrugated sheet stacks 6 into full stacks 52, which are then conveyed in a straight line by a floor conveyor (typically top of conveyor rollers approximately 12 inches above the floor) to another machine. These full stacks 52 are often created by first placing down a pallet 51 and/or a protective sheet on said sheet material removal system 7,7′. These protective sheets are often referred to as dunnage 50 in the industry. The pallet 51 and/or dunnage 50 provides protection, for the bottom sheets of the full stacks 52 and/or allow machinery down stream (typically fork lift trucks) to be able to handle the full stacks 52.
One form of sheet stacker 2 found in U.S. Pat. No. 2,901,250 granted to Martin on Aug. 25, 1959. The sheet stacker is typical of a class of stackers referred to as “upstackers” in the industry since they create a full stack 52 by using a stacking deck 3 which articulates in such a way that the receiving end has little or no vertical motion and the discharge end 4 has adequate motion to create full stacks 52 while moving in a generally upward motion. The cardboard/corrugated is transported on a plurality of conveyor belts built into the stacking deck 3 from the receiving end of the stacking deck 3 to the discharge end 4 of the stacking deck 3.
A second form of sheet stacker is found in U.S. Pat. No. 5,026,249 granted to TEI on Jun. 25, 1991. The sheet stacker is typical of a class of stackers referred to as a “downstackers” in the industry since they create a full stack 52 by elevating and lowering the sheet material removal system 7′ under a fixed stacking deck in such a way that the receiving end and discharge end of a stacking deck has no motion but the elevating conveyor lowers as the sheet stack 6 is created in order to create full stacks 52.
A third form of sheet stacker is a hybrid where both the stacking deck 2 and sheet material removal system 7′ can move in their prescribed motion in order to create the sheet stacks 6.
It is also common to stack cardboard/corrugated sheets into short sheet stacks 6 referred to as bundles in the industry. The bundles are typically created at the discharge end 4,4′ of the sheet stacker 2,2′ on some sort of conveyor roller or conveyor belt system, which is typically referred to as a bundle takeaway system. Typical bundle takeaway systems are waist high in order to allow the operator to manually manipulate the bundles down stream.
In both situations where full stacks 52 or bundles are being created, the sheets are stacked during the motion by which the variable pinch point gap 9,9′ between the discharge end 4,4′ of the stacking deck 3,3′ is increasing. Once a full stack 52 or bundle has been created, it must be transported from under the discharge end 4,4′ of the sheet stacker 2,2′. While the full stack(s) 52 or bundle(s) is being transported, an accumulation device 54 is often employed to collect sheetmaterial 5 so as to allow material to continue to fall off the end of the stacking deck 3,3′ while waiting for the full stack 52 or bundle to be transported and allowing the stacking deck 3,3′ and/or sheet material removal system 7,7′ to move towards each other, thus decreasing the variable pinch point gap 9,9′. One form of accumulation device 54 is found in U.S. Pat. No. 6,042,108, Morgan et al, granted Mar. 28, 2000. The variable pinch point gap must decrease in a relatively fast motion approximately 4–5 seconds on full stacks 52 and 1–2 seconds on bundles in order to keep the material collecting in the accumulator area 55 from exceeding the designed capacity of the accumulation device 54. The ejecting of a sheet stack and reduction of variable pinch point gap 9,9′ so next sheet stack can be built is commonly referred to as the load change cycle 56 in the industry.
This rapid motion of the stacking deck 3 and/or sheet material removal system 7′ to within close proximity results in a hazardous condition where the variable pinch point gap 9,9′ is formed between the bottom side of the discharge end 4,4′ of the stacking deck 3,3′ and the sheet material removal system floor conveyor or bundle takeaway system. Due to the weight and strength of the machinery, a person caught in this variable pinch point gap 9,9′ may have the result of serious injuries or death.
The open design of the stacking deck 3,3′ is a major productivity advantage of the sheet stacker 2,2′. During normal production it is important that the operator 50 have easy access to the discharge end 4,4′ of the stacking deck 3,3′. This invention targets the production operations performed by the operator. The production operations includes setting up the order, running the order, adjusting the order, checking for quality control purposes, placing dunnage 50 and/or pallets 51, clearing jams and placing stack identification tags into full stacks 52. While executing production operations the operator must be able to have access to the discharge end 4,4′ of the stacking deck 3,3′ without completely de-energizing and re-energizing the machinery since this would have a substantial impact on production.
The maintenance/clean up operations performed by the operator 30 and other employees is a different type of operation. Unlike the production operation where one individual is responsible for the area around the discharge end 4,4′ of the stacking deck 3,3′, the maintenance/clean up operations may involve one or more people sometimes working on key systems including the hydraulic, pneumatic and electrical systems. Most companies owning sheet stacking machinery have already established procedures, commonly referred to as Zero Energy State and/or Lock-Out-Tag-Out. These procedures require too much recovery time to use as a safety solution during production operations.
The ability of the stacking deck 3 and/or sheet material removal system 7′ to be able to execute a load change cycle 56 fully automatically without the assistance of the operator is often a required productivity feature of a sheet stacker 2,2′. Prior to this invention, some sheet stacker 2,2′ owners have elected to eliminate the ability of the operator to execute a load change cycle 56 fully automatically. These sheet stackers 2,2′ may require the operator to manually initiate the stacking deck 3,3′ down motion or to depress some sort of push button during the entire time the variable pinch point gap 9,9′ is decreasing. Even if this does not hinder the productivity due to the configuration of the sheet stacker 2,2′ production line, this solution still may not meet the guidelines of the International Safety Standards which include redundancy and self-testing.
A light guard system for this type of sheet stacker 2,2′ has been available since 1990 as provided by the Geo. M. Martin Co., see FIG. 1–4. However, this system has many short comings including 1) lack of a failsafe mode should a single component fail, 2) no self testing, 3) difficult installation and maintenance due to stringent mirror alignment requirements, 4) lack of flexibility when needing multiple mirrors to reflect the light, 5) no fault detection of cross talk from external optical sources, 6) interference due to light stand locations and 7) not able to run fully automatic cycling of full stacks 52 when the sheet stacker 2,2′ is equipped with an automatic dunnage 50 and/or pallet 51 system.